1. Field of the Invention
The present invention relates to an image sensor unit, an image reading apparatus, and an image forming apparatus. Particularly, the present invention relates to an image sensor unit, an image reading apparatus, and an image forming apparatus used to read a large original (large-sized original) and the like.
2. Description of the Related Art
Readable lengths (hereinafter, “read lengths”) of originals are generally about A4, B4, and A3 sizes in an image sensor unit used in an image reading apparatus or an image forming apparatus. In recent years, an elongated image sensor unit that can read large originals in A2, A1, and A0 sizes exceeding the read length of A3 size is used in an image reading apparatus, such as an electronic white board.
In the elongated image sensor unit, a plurality of short sensor substrates can be connected in a main-scan direction, or a plurality of short rod-lens arrays can be connected in the main-scan direction to reduce cost. Patent Document 1 discloses an image sensor including a plurality of short rod-lens arrays that are continuously arranged throughout a predetermined read length.    Patent Document 1: Japanese Laid-open Patent Publication No. 2005-217630
In the image sensor unit used in an electronic white board and the like, an image to be read includes large characters, and reading accuracy is not a problem. However, in an image sensor unit or the like used to read a large map and the like, fine reading accuracy is demanded as in reading of an original in general size.
When a plurality of short sensor substrates and a plurality of short rod-lens arrays are connected to the image sensor unit that requires fine reading accuracy, the sensor substrates to be connected and the rod-lens arrays to be connected need to be accurately connected. On the other hand, even if the sensor substrates to be connected and the rod-lens arrays to be connected are connected within an acceptable connection error, there is a problem that the reading accuracy is reduced in some cases if connection positions between the sensor substrates and connection positions between the rod-lens arrays are closely arranged.